Intervertebral implant, insertion tool and method of inserting same

ABSTRACT

An intervertebral implant, alone and in combination with an insertion tool for inserting same and a method for inserting same. The implant has upper and lower parts which have universal movement relative to each other. Each of the upper and lower parts also has a surface engaging an adjacent vertebrae. Each part has a keel extending from said surface into a cutout in the adjacent vertebrae, and each keel has an anterior opening recess therein. An insert tool has a pair of arms which are received in the recess of the keels through the anterior opening to securely hold and insert the implant. Projections and matching indentations in each arm and the base of its recess securely attached each arm within its keel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/669,273 filed Jan. 31, 2007 which is a continuation of applicationSer. No. 10/318,078 filed Dec. 13, 2002, the disclosure of which ishereby incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

This invention relates to intervertebral implants, and in particular, toa new and improved intervertebral implant and to an insertion tool and amethod for inserting same.

BACKGROUND OF THE INVENTION

Historically, when it was necessary to completely remove a disc frombetween adjacent vertebrae, the normal remedy was to fuse the adjacentvertebrae together. More recently, there have been importantdevelopments in the field of disc replacement, namely disc arthroplastywhich involves the insertion of an artificial intervertebral implantinto the intervertebral space between adjacent vertebrae and whichallows movement of the adjacent vertebrae relative to each other inflexion, extension, lateral bending, axial rotation and translation, aswell as absorbing axial compression.

One such development is an artificial intervertebral implant as shown inPublished Application No. WO 01/01893, published Jan. 11, 2001. Theinstruments for inserting same are shown in Published Application No. WO01/19295, published Mar. 22, 2001.

While the intervertebral implant and instruments as shown in thesepublications represents a substantial improvement in the art, thereexists a continuing need for improvements in the field of artificialintervertebral implants.

One such area in need of further improvements includes intervertebralimplants for the intervertebral spaces between adjacent cervicalvertebrae. This is because the cervical vertebrae and the dimensions ofthe intervertebral spaces between them are quite small. For example, thearea of the cervical vertebral surfaces facing the adjacent cervicalintervertebral spaces may be only about 20 percent of the intervertebralsurfaces of the vertebrae in the lumbar region, thereby making this anextremely delicate area in which to insert an intervertebral implant.

BRIEF SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a new and improvedintervertebral implant, an insertion tool and a method for insertingsame which are highly advantageous in the delicate and difficult area ofthe cervical spine. It is to be noted, however, that while the presentinvention has been developed particularly for the cervical spine, theinvention is equally applicable for inserting an intervertebral implantat any location in the spine, including the lumbar spine.

Thus, although the invention has been developed and is particularlyadvantageous for the cervical spine, it will be described below moregenerally as an intervertebral implant without specifically identifyingany particular portion of the spine.

It is thus an object of the present invention to provide a new andimproved intervertebral implant together with an insertion tool and amethod for inserting same.

It is another object of the present invention to provide an insertiontool and a method for inserting the new improved intervertebral implant.

In accordance with the present invention, there is provided anintervertebral implant having an upper part and a lower part which areoperatively engaged for limited universal movement relative to eachother. The upper part has a keel which is received in a cutout in theadjacent vertebrae, while the lower part has a keel which is received ina cutout in the other adjacent vertebrae. In accordance with a mainfeature of the present invention, these keels, in addition to providingan anchoring function within the adjacent vertebrae, include a recessopen at an end thereof for receiving arms of an insertion tool. This hasthe advantage of allowing grasping the implant firmly but over a verylimited area for inserting the implant into the intervertebral spacewith minimal invasion of the work area by the insertion tool.

The upper part preferably has a spherical concave portion formed in itslower surface. The lower part preferably has a plastic inlay attachedthereto, which inlay has a raised spherical convex portion which engagesthe spherical concave portion of the upper part to provide the limiteduniversal movement between the two.

The insertion tool usable in combination with the implant preferably hasa pair of arms, each of which engages a recess within a keel, each armhaving a projection which is moved toward the base of the recess toengage indentations in the base of the recesses to firmly hold theimplant. The arms also include lateral support portions which engagesupport cutouts on the upper and lower parts to absorb lateral forcesexerted on the implant so that such lateral forces do not have to beabsorbed by the more delicate portions of the insertion tool armslocated within the recesses of the keels.

The method of present invention comprises engaging an intervertebralimplant of the type described with an insertion tool of the typedescribed, inserting the intervertebral implant into the intervertebralspace with the keels entering cutouts in the adjacent vertebrae, andthen removing the insertion tool from the intervertebral implant,leaving the intervertebral implant in place within the intervertebralspace.

Thus, it is an object of the present invention to provide a new andimproved intervertebral implant.

It is another object of the present invention to provide an insertiontool and a method for inserting the new improved intervertebral implant.

It is another object of the present invention to provide anintervertebral implant which is particularly suitable for the cervicalspine.

It is another object of the present invention to provide a new andimproved intervertebral implant characterized by a recess in raisedkeels for receiving insertion tools for inserting the intervertebralimplant.

These and other objects of the present invention will be apparent fromthe detailed description to follow, together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described by way ofexample with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of an intervertebral implant in accordancewith the present invention;

FIG. 2 is a front elevational view of the implant of FIG. 1;

FIG. 3 is a left side elevational view of the implant of FIG. 1;

FIG. 4 is a cross sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a cross sectional view taken along line 5-5 of FIG. 3;

FIG. 6 is a top plan view of the upper part of the implant of FIG. 1;

FIG. 7 is a perspective view of the bottom surface of the upper part ofthe implant of FIG. 1;

FIG. 8 is a bottom plan view of the lower part of the implant of FIG. 1;

FIG. 9 is a bottom perspective view of the lower part of the implant ofFIG. 1;

FIG. 10 is a top perspective view of the lower part of the implant ofFIG. 1;

FIG. 11 is a top perspective view of the plastic inlay of the implant ofFIG. 1;

FIG. 12 is a top plan view of the plastic inlay of the implant of FIG.1;

FIG. 13 is a bottom perspective view of the plastic inlay of the implantof FIG. 1;

FIGS. 14-17 are elevational views of the implant of FIG. 1 illustratingthe limited universal movement of the parts thereof;

FIG. 18 is a schematic view of a pair of adjacent vertebrae prepared toreceive an implant of the present invention in the intervertebral spacetherebetween;

FIG. 19 illustrates the vertebrae of FIG. 18, in a direction along line19-19 of FIG. 18 and showing the implant itself about to be inserted andshowing an insertion tool prior to engaging the implant;

FIG. 20 illustrates a portion of an insertion tool for use with theimplant of the present invention;

FIG. 21 illustrates the vertebrae of FIG. 18 with the implant in placetherein and the insertion tool still holding the implant in the sameposition in which it held the implant during insertion; and

FIG. 22 illustrates the vertebrae with the implant in place and theinsertion tool removed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the figures, like elements are represented by likenumerals throughout the several views.

In this application, the words “upper” or “lower” or “uppermost” or“lowermost” or any other words describing the orientation of theintervertebral implant of the present invention are used only forconvenience and are not intended to convey any limitation. Morespecifically, the part of the implant described in this application asthe upper part can in fact be positioned as the superior or inferiorpart within the patient's vertebrae with the other of the two partsbeing the opposite part. Also, since the intervertebral implant isnormally inserted from the front of the patient, the side of thevertebrae toward which the intervertebral implant moves as it isinserted shall be referred to as the anterior side of the vertebrae andthe opposite side as the posterior side and the right and left sides aslateral sides. Since the more common manner of insertion is anteriorly,the present invention will be described with respect to thatorientation. Also, the posterior end of the implant may be referred toas the first end and the anterior end of the implant may be referred toas the second end. However, it is to be understood that theintervertebral implant can also be inserted laterally, i.e., from theside, in which case the keels will be oriented on the implant for suchlateral movement and the cutouts in the adjacent vertebrae will be opentoward a lateral side to receive the keel.

FIGS. 1-5 illustrate in different views the assembled intervertebralimplant 10 including an upper part, or component, 11, a lower part, orcomponent, 30 and a plastic inlay, or insert, 50 located therebetweenbut connected to the lower part 30.

The intervertebral implant of the present invention has been designedprimarily for insertion in the cervical spine. This portion of the spineis characterized by the need for precision because of the relativelysmall dimensions of the cervical intervertebral space. For example, theimplant of the present invention, when viewed in plan view (as best seenfor example in FIG. 6) would be approximately 12-16 millimeters in widthand approximately 15-19 millimeters in length. It has been foundpractical to provide three sizes, 12 millimeters×15 millimeters, 14millimeters×17 millimeters and 16 millimeters×19 millimeters. The heightof the implant, meaning the height from the upper surface of the upperpart to the lower surface of the lower part, excluding the keels, wouldnormally be between 5 millimeters and 9 millimeters. These dimensionsare in contrast to an intervertebral disc to be located in the lumbararea wherein the rectangular portion would have dimensions more on theorder of 27 to 30 millimeters in width, 34 to 39 millimeters in length,and a height of about 10 to 14 millimeters. However, it is to beunderstood that the features of the present invention are equallyadaptable for an intervertebral implant of a different size and designfor construction in any other part of the spine including the lumbarspine.

The upper part 11 will now be described in detail with respect to FIGS.1-5 which illustrate the assembled implant and FIGS. 6 and 7 whichillustrate only the upper part 11. The upper part 11 includes an uppersurface, or outer side, 12 which engages and supports the adjacentvertebral surface. This upper surface 12 is bounded by edges which areslightly beveled all the way around as shown at 13 with the largestportion of this bevel being along the posterior surface. Below thebeveled edge 13, the upper part is bounded by a surrounding side wall 14which has an anterior support cutout 15. Thus, in the figures the keelsare shown oriented anterior to posterior with the solid portion of thekeels facing posteriorly and the insertion engaging recess structurefacing anteriorly.

Rising above the upper surface 12 of the upper part 11 is a keel 16which includes a recess 17 formed therein. This recess is openedupwardly and anteriorly. Referring to FIGS. 4 and 6, this recessincludes an indentation 21 in the base thereof. The posterior end of thekeel 16 comprises a V-shaped upper bevel 19 and a V-shaped verticalportion 20, providing a front which is “arrow” shaped, as best seen inFIG. 6. The purpose of this “arrow” shape is to facilitate insertion ofthe keel into a cutout formed in the adjacent vertebrae. The anterioropening of the recess is flared at 18, which flare serves to anchor theanterior end of the keel 16 in its cutout in the adjacent vertebrae.

The upper part 11 includes a lower plane inner surface 24 whichincludes, as best seen in FIG. 7, a raised rim 26 which defines arounded surface such as a concave spherical portion 25, which surface,along with a mating surface, provide for universal movement relative toeach other. As best shown in FIGS. 4 and 5, this spherical concaveportion 25 will mate with an upper convex surface of the plastic inlay50.

The lower part 30 is described with reference to FIGS. 1-5 and alsoFIGS. 8-10 which show isolated views of the lower part 30.

The lower part 30 includes a lower vertebrae supporting and engagingsurface, or outer side, 31 and an inner upper surface 32. As best seenin FIGS. 2, 5 and 10, this lower part includes grooves 33 and 34 formedin the interior side wall thereof beneath surface 32 and above a basesurface 38. A substantially flat back wall 35 extends from base surface38 to upper surface 32. This lower part includes a beveled edge 36extending around the periphery of the lower surface 31 with a mostpronounced bevel at the posterior thereof and a surrounding side wall39. The purpose of the grooves 33 and 34 is to receive side flanges 53and 54 of a plastic inlay 50, as shown in FIG. 11 and as will bedescribed in greater detail below.

Lower part 30 includes an anterior support cutout 37. A keel 40 risesupwardly (or in the usual orientation, extends downwardly) from thelower surface 31. This keel includes a recess 41 which opens downwardlyand anteriorly and has a flared anterior entrance to the recess at 42,which flared entrance serves the same function as flared entrance 18 ofupper part 11, i.e., to facilitate engagement of the anterior end of thekeel within its cutout in the vertebrae. As best shown in FIG. 4, therecess 41 opens downwardly and anteriorly and includes an indentation43. The keel 40 includes at its posterior end a V-shaped lower bevel 45and a V-shaped vertical portion 46 which together provide an “arrow”shape, as best seen in FIG. 8 to facilitate insertion of the keel intoits cutout formed in the adjacent vertebrae. As seen in the figures, therecesses run along an anterior-posterior line of the implant.

Referring momentarily to FIG. 13, it will be noted that the lowersurface of the plastic inlay 50 includes a raised snap-in projection 57.Referring now to FIG. 10, there is illustrated a snap-in recess 44 whichis adapted to receive the snap-in projection 57 such that the plasticinlay can snap into place but is thereafter prevented from beingremoved. This snap fit is also shown clearly in FIG. 4. It will benoted, however, that while removal would not occur under normalcircumstances, in fact it is possible at a subsequent time, by insertinga tool between the base of the lower part and the plastic inlay to prythe plastic inlay out and remove it. This might be useful, for example,if it were decided to insert a new plastic inlay of a different size orif it became necessary to repair the previously inserted plastic inlay.

The upper and lower parts are made of a suitable material such astitanium, cobalt chromium molybdenum, stainless steel or ceramics. Theupper surface of the upper part and the lower surface of the lower partas well as the side surfaces of the keels are coated with a porouscoating of titanium. The porosity of the coating ideally permitsvascularization and osteoplast formation with subsequent bony on-growth.

The plastic inlay 50 is visible in FIGS. 1-5. However, for conveniencethe numerals pointing to details thereof are not included in any ofthose figures, but instead are provided in FIGS. 11-13. It is preferablymade of high density polyethylene. FIG. 11 illustrates the plastic inlay50 in its position as shown in FIG. 1. It includes a flat upper surface51 having attached thereto a rounded surface such as a convex sphericalportion 52, which surface mates with the concave spherical portion 25 ofthe upper part 11 to provide for universal movement. Side flanges 53 and54 engage the grooves 33 and 34 in the lower part 30. A flat posteriorwall 55 engages the posterior wall 35 of the lower part.

Referring to FIG. 13, the plastic inlay 50 includes a generally flatlower surface 56 which engages the base surface 38 of the lower part anda snap-in projection 57 which is beveled on the posterior side andincludes a sharp ledge on the anterior side so as to snap into place inthe recess 44 of base surface 38 to the position as best shown in FIG.4.

FIGS. 14-17 illustrate the limited universal movement of the upper andlower parts of the implant relative to each other when inserted in apatient's intervertebral space. FIGS. 14 and 15, both of which view theanterior of the implant, show maximum lateral bending to the left andright, respectively. It will be noted that in each case the raised rim26 of the upper part 11 engages the inner surface 32 of the lower part30. In a preferred embodiment, such lateral bending movement is possiblefor up to approximately 10.5° for the smaller of the three sizes andapproximately 8.9° for the two larger sizes, relative to a referenceposition wherein the keels are aligned vertically. FIG. 16, which showsa view from the right side of the patient, shows extension movement ofthe upper part relative to the lower part which is limited by engagementof the rim 26 with the inner surface 32 of the lower part 30. Finally,FIG. 17, which is a view from the patient's left side, shows maximumflexion of the upper part 11 relative to the lower part 30. Flexion islimited by engagement of the rim 26 with the surface 51 of the inlay 50.In preferred embodiments, extension and flexion can occur up toapproximately 10.5° for the smaller three sizes and approximately 8.9°for the two larger sizes, relative to a reference position wherein thekeels are vertically aligned. As is apparent from the precedingdiscussion, the term “limited” as applied to universal movement refersto the limited range in each direction, as described above. However, asis also apparent, within that range, the movement is conventionaluniversal movement in the sense that movement is allowed in alldirections.

FIGS. 18-22 illustrate the method of insertion of the implant shown inFIGS. 1-17 and a portion of a handling instrument such as an insertiontool for use for inserting the implant.

FIG. 18 is an anterior view of a pair of adjacent vertebrae V onopposite sides of a cleaned-out intervertebral space I. In preparationfor inserting the intervertebral implant of the present invention,cutouts C will be formed in the vertebrae V. As shown in FIG. 18 and theleft hand portion of FIG. 19, these cutouts start from the anterior ofthe vertebrae and extend for most but not all of the distance toward theposterior of the vertebrae, intersecting along its entire length withthe surface of the vertebrae facing into the intervertebral space.

FIG. 19 illustrates just to the right of the prepared adjacent vertebraethe intervertebral implant assembled in the form as shown in FIGS. 1-5.To the right thereof is an insertion tool 60 which is to be describedwith respect to FIGS. 19 and 20. This insertion tool 60 includes anupper arm 61 and a lower arm 71, which arms are arranged to move towardsand away from each other as indicated by the arrows B in FIG. 19.Various devices can be provided for moving these arms towards and awayfrom each other. One such mechanism in the form of a scissors ispartially shown at 80 in FIG. 20. The upper and lower arms include keelengaging portions 62 and 72 which engage recesses 17 and 41,respectively. These arms include towards their outer ends projections 63and 73 which are constructed to be received in the indentations 21 and43, respectively. It will be noted that these keel engaging portions 62and 72 are relatively narrow. In fact, it is contemplated that theentire width of each keel will be approximately 2 millimeters, thusallowing less than 2 millimeters for the actual recesses. The arms 61and 71 also include lateral support surfaces 64 and 74 which, uponengagement of the tool with the implant, will engage the front supportcutouts 15 and 37.

The arms 61 and 71 will be spaced apart from each other just enough forthe projections 63 and 73 to clear the bottoms of the recesses 17 and 41until the projections 63 and 73 reach the indentations 21 and 43, atwhich time the arms 61 and 71 will be moved towards each other such thatthe projections 63 and 73 engage within the indentations 21 and 43 andthe lateral support surfaces 64 and 74 are engaged within the cutouts 15and 37. At this position, abutment surfaces 65 and 75 on the upper armand lower arm 61 and 71, respectively, will abut each other, thuslimiting further movement of the arms 61 and 71 towards each other.

With the assembled implant thus attached to the insertion tool, theinsertion tool moves it into the intervertebral space with the keels 16and 40 entering the cutouts C, while the portions of the upper and lowerparts 11 and 30 posterior of the keels extends within the intervertebralspace beyond the cutouts C so that upper surface 12 engages theintervertebral surface of the adjacent vertebrae V posterior of andadjacent to the keel 16 and surface 31 of the lower part 30 engages theintervertebral surface of the adjacent lower vertebrae posterior andadjacent to the keel 40. Actually, the above described engagement of theinsertion tool 60 and the implant 10 prior to insertion is the same asshown in FIG. 21, just after insertion.

It will be noted that in FIG. 21 there is a space above and below thearms 61 and 71 within keel recesses 17 and 41, the vertical dimension ofwhich spaces is greater than the height of the projection 63 and 73,which would normally be about 1.2 millimeters. This is necessary so thatthe arms 61 and 71 can be moved upwardly and downwardly, respectively,away from the base of their respective recesses to free the projectionsfrom the indentations before the upper and lower surfaces of arms 61 and71 engage the vertebrae at the vertical extremities of the cutouts C.Such contact is to be avoided. Once these arms have been separatedaccordingly, they can be moved out from the implant, anteriorly, leavingthe implant in place as shown in FIG. 22.

The method of the present invention will be apparent from the abovedescribed operation of the invention as shown and described with respectto FIGS. 18-22. In accordance with this method of the present invention,adjacent vertebrae are provided with cutouts in the manner described andan intervertebral implant of the type described is grasped with aninsertion tool having arms which are received in the recesses of thekeels through the anterior openings thereof. With the implant firmlygrasped by the insertion tool, the implant is inserted anteriorly withthe keels leading the way into the cutouts until the proper position hasbeen reached. At this time, naturally some force will have been exertedto distend the adjacent vertebrae from each other, but preferably justenough to allow the implant to be inserted. In fact, many professionalsprefer to distend the adjacent vertebrae no more than essentially thewidth between the upper and lower surfaces 12 and 31 and then applyadditional external force with a mallet or the like to completeinsertion of the implant. After the implant has been inserted, the armsof the insertion tool are separated just enough to free theprojection/indentation engagements from each other, whereupon theinsertion tool is removed anteriorly, leaving the implant in place andrelieving any previously applied forces applied to distend the adjacentvertebrae from each other, allowing these adjacent vertebrae to restupon the supporting surfaces 12 and 31 of the implant.

Although the invention has been described in detail with respect topreferred embodiments thereof, it will be apparent to one skilled in theart that the invention is capable of numerous modifications andvariations within the spirit and scope of the invention.

What is claimed:
 1. In combination, an intervertebral implant and ahandling instrument, the combination comprising: the implant including:an upper part having an upper surface that is adapted to engage a firstvertebra that is spaced from a second vertebra so as to define anintervertebral space therebetween; and a lower part in operativeengagement with the upper part such that the upper and lower parts aremovable relative to each other, the lower part having a lower surfacethat is adapted to engage the second vertebra, wherein each of the upperpart and lower part defines a trailing end and a leading end that isspaced from the trailing end along an insertion direction into theintervertebral space; the upper part including an upper keel thatincludes first and second side walls that each extend out from the uppersurface such that when the implant is inserted into the intervertebralspace, the upper keel is positioned at least partially within a cutoutformed in the upper vertebra; and the lower part including a lower keelthat includes first and second side walls that each extend out from thelower surface such that when the implant is inserted into theintervertebral space, the lower keel is positioned at least partiallywithin a cutout formed in the lower vertebra; wherein the implantincludes an upper recess partially defined by the side walls of theupper keel, and a lower recess partially defined by the side walls ofthe lower keel, and the upper and lower recesses extend into theirrespective keels along the insertion direction and terminate withintheir respective keels such that the upper and lower recesses are closedto the respective leading end and open to the respective trailing end;and the handling instrument including: an upper arm and a lower arm thatare configured to be inserted into the upper and lower recesses,respectively, along the insertion direction such that the handlinginstrument holds the implant during insertion of the implant into theintervertebral space.
 2. The combination as recited in claim 1, whereinthe implant further comprises an insert disposed between the upper partand the lower part, the insert connecting the upper part and the lowerpart so as to permit relative movement between the upper part and thelower part.
 3. The combination as recited in claim 2, wherein the insertincludes a rounded surface, and the insert rounded surface mates with arounded surface of one of the upper part or the lower part to providethe relative movement between the upper part and the lower part.
 4. Thecombination as recited in claim 3, wherein the mated rounded surfacesprovide limited universal movement between the upper part and the lowerpart.
 5. The combination as recited in claim 1, wherein the upper partand the lower part move relative to each other along a rounded matingsurface.
 6. The combination as recited in claim 5, wherein the roundedmating surface provides limited universal movement between the upperpart and the lower part.
 7. The combination as recited in claim 1,wherein the upper recess and the upper arm have corresponding shapes,and wherein the lower recess and the lower arm have correspondingshapes.
 8. The combination as recited in claim 1, wherein the upper andlower recesses are configured to receive the handling instrument suchthat the handling instrument does not contact the first vertebra or thesecond vertebra during insertion of the implant into the intervertebralspace.
 9. The combination as recited in claim 1, wherein the handlinginstrument is an insertion tool.
 10. The combination as recited in claim1, wherein the upper keel and the lower keel each define a trailing endand a leading end spaced from the trailing end along the insertiondirection, the leading end of the upper keel is offset from the leadingend of the upper part in a direction opposite the insertion direction,and the leading end of the lower keel is offset from the leading end ofthe lower part in the direction opposite the insertion direction. 11.The combination as recited in claim 10, wherein the trailing end of theupper keel is offset from the trailing end of the upper part in theinsertion direction, and the trailing end of the lower keel is offsetfrom the trailing end of the lower part in the insertion direction. 12.The combination as recited in claim 1, wherein the upper keel and thelower keel each define a trailing end and a leading end spaced from thetrailing end along the insertion direction, the trailing end of theupper keel is offset from the trailing end of the upper part in theinsertion direction, and the trailing end of the lower keel is offsetfrom the trailing end of the lower part in the insertion direction. 13.In combination, an intervertebral implant and a handling instrument, thecombination comprising: the implant including: an upper part having anupper surface that is adapted to engage a first vertebra that is spacedfrom a second vertebra so as to define an intervertebral spacetherebetween, the upper part further having a pair of opposed sidesurfaces that define a width of the upper part; and a lower part inoperative engagement with the upper part such that each of the upper andlower parts is movable relative to the other of the upper and lowerparts, the lower part having a lower surface that is adapted to engagethe second vertebra, the lower part further having a pair of opposedside surfaces that define a width of the lower part, wherein the upperand lower parts are separate parts, each of the upper part and the lowerpart defines a trailing end and a leading end that is spaced from thetrailing end along an insertion direction into the intervertebral space,the width of the upper part and the width of the lower part each beingmeasured in a first direction that is perpendicular to the insertiondirection; and the upper part further including an upper keel, the upperkeel including a first keel side wall and a second keel side wall thatis spaced from the first keel side wall in the first direction, theupper keel defining a maximum upper keel width measured from the firstkeel side wall to the second keel side wall in the first direction, themaximum upper keel width being less than the width of the upper part,the upper keel further including a first base and a first tip that isspaced from the first base in a second direction that is substantiallyperpendicular to both the insertion direction and the first direction,the first base extends from the upper surface such that the upper keelextends out from the upper surface in the second direction andterminates at the first tip, the upper keel being at least partiallyinsertable into the intervertebral space; and the lower part furtherincluding a lower keel, the lower keel including a third keel side walland a fourth keel side wall that is spaced from the third keel side wallin the first direction, the lower keel defining a maximum lower keelwidth measured from the third keel side wall to the fourth keel sidewall in the first direction, the maximum lower keel width being lessthan the width of the lower part, the lower keel further including asecond base and a second tip that is spaced from the second base in adirection that is opposite the second direction, the second base extendsfrom the lower surface such that the lower keel extends out from thelower surface in the direction opposite the second direction andterminates at the second tip, the lower keel being at least partiallyinsertable into the intervertebral space; wherein the first keel sidewall and the second keel side wall partially define an upper recess thatis open to the trailing end of the upper part, and the third keel sidewall and the fourth keel side wall partially define a lower recess thatis open to the trailing end of the lower part; the handling instrumentincluding: an upper arm and a lower arm that are configured to beinserted into the upper and the lower recesses respectively, along theinsertion direction such that the handling instrument holds the implantduring insertion of the implant into the intervertebral space.
 14. Thecombination as recited in claim 13, wherein the upper part and the lowerpart move relative to each other along a rounded mating surface.
 15. Thecombination as recited in claim 14, wherein the rounded mating surfaceprovides limited universal movement between the upper part and the lowerpart.
 16. The combination as recited in claim 13, wherein the implantfurther comprises an insert disposed between the upper part and thelower part, the insert connecting the upper part and the lower part soas to permit relative movement between the upper part and the lowerpart.
 17. The combination as recited in claim 16, wherein the insertincludes a rounded surface, and the insert rounded surface mates with arounded surface of one of the upper part or the lower part to providethe relative movement between the upper part and the lower part.
 18. Thecombination as recited in claim 17, wherein the mated rounded surfacesprovide limited universal movement between the upper part and the lowerpart.
 19. The combination as recited in claim 13, wherein the upperrecess and the upper arm have corresponding shapes, and wherein thelower recess and the lower arm have corresponding shapes.
 20. Thecombination as recited in claim 13, wherein the upper and lower recessesare configured to receive the handling instrument such that the handlinginstrument does not contact the first vertebra or the second vertebraduring insertion of the implant into the intervertebral space.
 21. Thecombination as recited in claim 13, wherein the handling instrument isan insertion tool.
 22. The combination as recited in claim 13, whereinthe upper recess terminates within the upper part at a location betweenthe leading end and the trailing end of the upper part, and the lowerrecess terminates within the lower part at a location between theleading end and the trailing end of the lower part.
 23. The combinationas recited in claim 13, wherein the upper recess is positioned at leastpartially between the first base and the first tip, and the lower recessis positioned at least partially between the second base and the secondtip.
 24. The combination as recited in claim 13, wherein the upper keeland the lower keel each define a trailing end and a leading end spacedfrom the trailing end along the insertion direction, the leading end ofthe upper keel is offset from the leading end of the upper part in adirection opposite the insertion direction, and the leading end of thelower keel is offset from the leading end of the lower part in thedirection opposite the insertion direction.
 25. The combination asrecited in claim 24, wherein the trailing end of the upper keel isoffset from the trailing end of the upper part in the insertiondirection, and the trailing end of the lower keel is offset from thetrailing end of the lower part in the insertion direction.
 26. Thecombination as recited in claim 13, wherein the upper keel and the lowerkeel each define a trailing end and a leading end spaced from thetrailing end along the insertion direction, the trailing end of theupper keel is offset from the trailing end of the upper part in theinsertion direction, and the trailing end of the lower keel is offsetfrom the trailing end of the lower part in the insertion direction. 27.The combination as recited in claim 13, wherein the first and secondkeel side walls extend out from the upper surface at the first base, andthe third and fourth keel side walls extend out from the lower surfaceat the second base.
 28. In combination, an intervertebral implant and ahandling instrument, the combination comprising: the implant including:an upper part having an upper surface that is adapted to engage a firstvertebra that is spaced from a second vertebra so as to define anintervertebral space therebetween; and a lower part in operativeengagement with the upper part such that the upper and lower parts aremovable relative to each other, the lower part having a lower surfacethat is adapted to engage the second vertebra, wherein each of the upperpart and the lower part defines a trailing end and a leading end that isspaced from the trailing end along an insertion direction into theintervertebral space, the upper part defines an upper pair of sidesurfaces that are spaced from each other along a first direction that isperpendicular to the insertion direction, such that the upper pair ofside surfaces defines a width of the upper part, and the lower partdefines a lower pair of side surfaces that are spaced from each otheralong the first direction, such that the lower pair of side surfacesdefines a width of the lower part; the upper part including an upperkeel that includes first and second side walls that each extend out fromthe upper surface such that the upper keel is configured to bepositioned at least partially within a cutout formed in the uppervertebra when the implant is inserted into the intervertebral space; thelower part including a lower keel that includes first and second sidewalls that each extend out from the lower surface such that the lowerkeel is configured to be positioned at least partially within a cutoutformed in the lower vertebra when the implant is inserted into theintervertebral space, wherein the implant includes 1) an upper recessthat is defined by the upper part, disposed equidistantly between theupper pair of side surfaces along the first direction, is closed to theleading end of the upper part, and is open to the trailing end of theupper part, and 2) a lower recess that is defined by the lower part,disposed equidistantly between the lower pair of side surfaces along thefirst direction, is closed to the leading end of the lower part, and isopen to the trailing end of the lower part; and the handling instrumentincluding an upper arm that is configured to be inserted into the upperrecess along the insertion direction, and a lower arm that is configuredto be inserted into the lower recess along the insertion direction, suchthat the handling instrument holds the implant during insertion of theimplant into the intervertebral space.
 29. The combination as recited inclaim 28, wherein the upper keel and the lower keel each define atrailing end and a leading end spaced from the trailing end along theinsertion direction, the leading end of the upper keel is offset fromthe leading end of the upper part in a direction opposite the insertiondirection, and the leading end of the lower keel is offset from theleading end of the lower part in the direction opposite the insertiondirection.
 30. The combination as recited in claim 29, wherein thetrailing end of the upper keel is offset from the trailing end of theupper part in the insertion direction, and the trailing end of the lowerkeel is offset from the trailing end of the lower part in the insertiondirection.
 31. The combination as recited in claim 28, wherein the upperkeel and the lower keel each define a trailing end and a leading endspaced from the trailing end along the insertion direction, the trailingend of the upper keel is offset from the trailing end of the upper partin the insertion direction, and the trailing end of the lower keel isoffset from the trailing end of the lower part in the insertiondirection.
 32. The combination as recited in claim 28, wherein: 1) theupper keel includes a first base and a first tip that is spaced from thefirst base in a second direction that is substantially perpendicular toboth the insertion direction and the first direction, the first base islocated adjacent the upper surface such that the upper keel extends outfrom the upper surface in the second direction and terminates at thefirst tip, and the upper recess is positioned at least partially betweenthe first base and the first tip, and 2) the lower keel includes asecond base and a second tip that is spaced from the second base in adirection opposite the second direction, the second base is locatedadjacent the lower surface such that the lower keel extends out from thelower surface in the direction opposite the second direction andterminates at the second tip, and the lower recess is positioned atleast partially between the second base and the second tip.
 33. Thecombination as recited in claim 28, wherein the implant furthercomprises an insert disposed between the upper part and the lower part,the insert connecting the upper part and the lower part so as to permitrelative movement between the upper part and the lower part.
 34. Thecombination as recited in claim 33, wherein the insert includes arounded surface, and the insert rounded surface mates with a roundedsurface of one of the upper part or the lower part to provide therelative movement between the upper part and the lower part.
 35. Thecombination as recited in claim 34, wherein the mated rounded surfacesprovide limited universal movement between the upper part and the lowerpart.
 36. The combination as recited in claim 28, wherein the upper partand the lower part move relative to each other along a rounded matingsurface.
 37. The combination as recited in claim 36, wherein the roundedmating surface provides limited universal movement between the upperpart and the lower part.
 38. The combination as recited in claim 28,wherein the upper recess and the upper arm have corresponding shapes,and wherein the lower recess and the lower arm have correspondingshapes.
 39. The combination as recited in claim 28, wherein the upperand lower recesses are configured to receive the handling instrumentsuch that the handling instrument does not contact the first vertebra orthe second vertebra during insertion of the implant into theintervertebral space.
 40. The combination as recited in claim 28,wherein the handling instrument is an insertion tool.
 41. Thecombination as recited in claim 28, wherein the upper recess ispartially defined by the first and second side walls of the upper keel,and the lower recess is partially defined by the first and second sidewalls of the lower keel.